Not only does the barn swallow (Hirundo rustica) have the distinction of being the most widely distributed and abundant of all swallows, it is also one of the most familiar bird species in the world. Having historically bred in caves, today it has almost completely converted to constructing its nest under the eaves of buildings, and it is this long association with human habitation that makes it quite so familiar, as well as earning the species its common name. This popular bird is admired for its supreme agility in flight, with a slender body, long, narrow, pointed wings, and a deeply-forked tail with long streamers allowing the barn swallow to spend most of its time on the wing. It has an attractive plumage of steely blue-black upperparts, red throat, and black wings and tail that sit in start contrast to pale underparts. The male and female bird are very similar in appearance, although the tail streamers tend to be longer on the male, but the juvenile has paler underparts and a less deeply forked tail.